Metallurgical apparatus – Means treating a continuum of work – With heating means
Reexamination Certificate
2000-08-11
2002-07-09
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means treating a continuum of work
With heating means
C266S249000
Reexamination Certificate
active
06416707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for producing fine wire, especially card wire, in which an optionally already treated, in particular, drawn, wire blank is transformed into a drawable state by a heat treatment process, is then drawn, and is subsequently hardened and tempered for obtaining predetermined mechanical properties; an apparatus for performing such a method; a furnace devices as well as a cooling device of such an apparatus.
2. Description of the Related Art
Card wires of unalloyed and alloyed steels produced with methods of the aforementioned kind are used, for example, for processing textile fibers in cards. For this purpose, the fine wires obtained by this method are further processed to sawtooth wires and, for example, applied to the card flat. For processing the textile fibers the swift of the card with an arrangement applied thereto is set into rotational motion about the cylinder axis so that the arrangement can pass through the supplied fiber material to clean it, wherein the flat arrangements of the stationary or oppositely driven flats interact with the swift arrangement. In this context, it must be ensured for obtaining a satisfactory processing quality that the card wire for all flats of the card has uniform mechanical properties. Moreover, the mechanical properties of the card wires must be maintained at a constantly high level over the total length of the sawtooth wire strips applied to the flats because local defects of the card wires would result in damage of the all-steel sawtooth wire arrangement formed thereof, and this would require a complete exchange. In the context of modern high-performance cards this is connected with very high costs with respect to the resulting machine downtimes and the material required therefor. On the other hand, the coil-shaped wires applied to the cylindrical swift and the total length of the sawtooth wire strips applied to the flat have a length of several hundred meters in modern high-performance cards. Accordingly, when performing a method for producing card wire it must be ensured that the resulting mechanical properties are constant over the entire length of several hundred meters. In the following a known method will be explained with which fine wires can be produced and which fulfills these requirements:
In this connection, first a so-called wire rod is produced and drawn to the elongation limit. The thus obtained drawn wire, however, has generally not yet a sufficiently minimal cross-sectional surface area in a sectional plane extending perpendicularly to the longitudinal direction. Accordingly, the obtained wire blank resulting from the first drawing process is conventionally subjected to a heat treatment process with which it again obtains a microstructure which makes the wire again processable, i.e., drawable.
During the course of this heat treatment process the wire blank in the known method is initially heated to a temperature in the range of 800 to 1,000° C. in which a microstructure transformation of the steel used as the wire material into the austenitic structure will result. Subsequently, the wire is then quenched to a temperature in the range of 400 to 600° C. and is kept at this temperature for a predetermined duration. When using steel as the material for the fine wire or card wire, this causes a microstructure transformation into the pearlitic structure which is characterized by its excellent cold forming properties. After completion of this transformation, the wire is again cooled to room temperature and subjected to a hardening and tempering process for obtaining the predetermined mechanical properties.
For heating the wire to a temperature of 800 to 1,000° C., conductive and inductive heating methods can be employed. In view of the very high energy costs and capital expenditure for furnaces for performing a conductive or inductive heating, the heating to a temperature of 800 to 1,000° C. is, however, carried out generally in electrically heated or gas-heated furnaces through which the wire blank is guided in respective pipes penetrating the furnaces. Such furnaces have the additional advantage that the temperature of the wire portions guided through the furnace can be better maintained at a constant level than with conductive or inductive wire heating, and this has a positive effect on the uniformness of the austenitic structure that can be obtained with this furnace.
For quenching the wire blank to the required temperature in the range of 400 to 600° C. for the microstructure transformation into the pearlitic structure and for maintaining the wire blank at this temperature, liquid lead is used traditionally. The use of liquid lead, however, is a problem because an oxidation of the wire blank at the interface liquid lead-air cannot be prevented and, furthermore, the wire blank passing through the liquid lead bath also entrains lead. This entrained lead must be removed from the wire and must be disposed of. A complete removal of the lead from the wire blank is however almost impossible. Accordingly, lead that is still remaining on the wire blank has a negative effect on the further drawing process and later on also on the surface quality of the card wire.
With respect to these problems in connection with using liquid lead for quenching and subsequent maintaining of the wire blank at the temperature of 400 to 600° C., it has already been suggested to perform this process in a fluidized bed. In such a fluidized bed flowable material, such as, for example, sand, is fluidized by means of compressed air introduced through a bottom of a corresponding fluidized chamber. When the wire blank passes through the resulting layer of fluidized flowable material, a quick cooling of the wire blank to the temperature of the flowable material results because the latter behaves in the fluidized state approximately like liquid and thus can quickly dissipate heat energy from the wire blank.
However, upon passing through the layer of fluidized flowable material, an undesirable oxide layer is formed on the wire blank which, although it is partially removed because of the abrasive effect of the sand conventionally used as a flowable material, then remains within the fluidized chamber. These so-called scale particles have a negative effect on the quenching behavior so that regular cleaning, respectively, regular exchange of the flowable material is required. Moreover, with this method it is also necessary to chemically remove or etch away oxide particles still remaining on the wire blank, the so-called residual scale.
The problems explained supra in connection with the use of fluidized beds occur in even greater form when the flowable material is heated to a temperature in the range of 400 to 600° C. for ensuring the desired microstructure transformation into the pearlitic structure because at these temperatures the formation of the oxide layer is favored and, additionally, combustion products of the conventionally employed gas burners for heating the flowable material will deposit on the wire blank.
For removing the foreign material remaining on the wire blank from the use of the lead bath as well as from the use of a fluidized bed, i.e., also the oxide layer referred to as scale layer, and the additional lead residues, depending on the employed method, a so-called etching device is conventionally used. Conventionally, it is comprised substantially of etching tanks, filled generally with hydrochloric acid or sulfuric acid, and several rinsing tanks through which the wire blank passes sequentially in a cascade-like manner as well as a drying device arranged downstream thereof.
The wire which has thus been returned to a processable, i.e., drawable, state is then drawn in a conventional drawing method in order to obtain the desired wire shape. Subsequently, the card wires must still be hardened and tempered for obtaining the required mechanical properties.
The hardening and tempering process is employed, in particular, in order to obtain for the already drawn wires a
Friedrich Kueffner
Graf + Cie AG
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